Mikhail Gorbachev knows about wars in Afghanistan. When he ruled the Soviet Union, he ended up bringing the mighty Red Army home, tails between their legs, after years of being sniped at by "insurgent" Afghans who didn't want their country imposed on by a superpower. Not long after, his own country broke up. Failing imperial wars aren't good for national budgets or stability at home. Now he has a warning for the United States.

"Victory is impossible in Afghanistan. Obama is right to pull the troops out. No matter how difficult it will be," Mr Gorbachev said.

He said before the Soviet Union withdrew from Afghanistan, an agreement had been reached with Iran, India, Pakistan and the US. "We had hoped America would abide by the agreement that we reached that Afghanistan should be a neutral, democratic country, that would have good relations with its neighbours and with both the US and the USSR.

"The Americans always said they supported this, but at the same time they were training militants - the same ones who today are terrorising Afghanistan and more and more of Pakistan," Mr Gorbachev said. Because of this, it would be more difficult for the US to get out of the situation.